1. Field of the Invention
The present invention relates to a press forming system for glass products such as optical lenses. The present invention is more particularly concerned with a structure of a transferring device for loading blanks and unloading formed products into and from the press forming system having a plurality of press units.
2. Description of the Related Art
Optical glass elements such as optical lenses are formed also by press forming other than polishing and grinding. In the press forming apparatus for glass, a blank of glass is placed between a pair of dies, heated to a temperature above the glass transition point, and press-formed by use of the dies, thereby transferring the pattern of the dies to the blank to form a product.
In the press forming apparatus for glass, a product is formed through a relatively long process comprising steps of placing a blank in dies, heating, press forming, cooling, opening the dies, and taking out a formed product from the dies. Therefore, to ensure the productivity, a plurality of press units is usually arranged in parallel. In such a case, a transfer machine for loading a blank and unloading a formed product is usually provided in every press unit. However, if the system is constructed as mentioned above, the footprint of the entire system will be increased.
In order to save the footprint, attempts were made to develop a press forming system for glass having a single transfer machine commonly used for gaining access to a plurality of press units. In this system, if there are a plurality of press units waiting for the same step to exchange a formed product for a new blank, other press units except one unit in which the exchanging step is first initiated, are put on standby. As a result, an actual availability of the entire system deteriorates.